Groaning over Beckenham, Kent

[Beckenham_Boy]

Hi Everyone, My name is Luis, I'm 10 & live in Beckenham, Kent (nr Biggin Hill). I think I'm under the approach to LHR as you start to pass over my bedroom at about 5am every day. My question is what is the loud groan that the aircraft make, like an elephant (seriously). I think it's only Boeings that do it (guessing from looking thru my binoculars). When I was on a 757 recently I heard the noise from inside the aircraft when I was sitting behind the wing on the approach.

Thanks a lot, especially Capt V from Easyjet who was very good at explaining things a while ago in Spain. Flight Sim going well cheers.

[frostbite]

Since none of those who might know have answered, I will make a guess that it's the landing gear being deployed.

[helicopter-redeye]

Probably a reconfiguration of some form, at Beckenham (Kent) most likely flaps than landing gear.

[Jetstream Rider]

Sometimes when you move the flaps, there is a groaning like you describe. You can hear it during flap retraction and deployment. I live a few miles from Heathrow and I fairly often hear it from aircraft on departure. From inside I can sometimes hear it too - usually going from flaps up to flap 1 (the first stage). I fly the B757 and 767 and I have heard it from overflying 747's. Not sure about Airbuses, I'll look out to see if it is a Boeing thing or not.

[FlyingTom]

I used to wonder the same thing. As a jet positions for an approach it is usually descending and decellerating and so the power is reduced to idle. As the aircraft achieves the final descent profile the flaps are selected and the total drag increases. The engines have to spool back up and start producing more thrust and I think that this is when you hear that groaning noise. It probably depends on where you are situated as I never hear it when the engines are spooled up for take off. Possibly the noise is radiated forwards from the compressors so you may have to be in front to here it.

Good question.

[Rainboe]

I was thinking about this one and down here on the south coast in Portsmouth, I hear it almost always from 757s at quite high altitude. I've thought it must be levelling off and spooling up. It is a most peculiar spool up noise at it passes bang overhead at least 10-12,000'. It makes people look.

[hec7or]

hi BB,

Believe it or not, back in the '70s we used to get the same thing, and we'd talk about it at school (Langley Park) in the morning before assembly, the conclusion we'd generally come to was that it was a BAC 1-11 at the same time each night, slowing down and deploying flap. They made a very peculiar noise!

As well as that, we often had lessons disrupted by VC10s climbing out on easterly flightpaths and you couldn't even hear your mates on the next table in the classroom shouting abuse at you over the roar of those Conways!!

Tridents could also be relied upon to bring a halt to nonsense like rugby lessons on cold (easterly winds) autumn mornings due to their stunningly poor climb performance and their earsplitting engine exhaust note.

All aircraft make odd noises at various points of the flight envelope and long may it continue!

[Beckenham_Boy]

Thanks a lot everyone, might be at Langley Park next year! Would be interested to know why Airbus don't do it tho if anyone has the time. It's def not the undercarriage, have only ever seen one plane with undercarriage down over Beckenham.

[Kak Klaxon]

Do all pilots come from Beckenham?

I went to Langley Park in the early 1980s and as a result I cant spell or write but I do have over 10000 hours now.

I too know the noise you are talking about,I have no idea what makes it though.

[ratarsedagain]

The 767 makes a fairly peculiar noise as you describe when you select flap 1 (but not as you select further stages). This would fit in with the location you describe, as aircraft leaving Biggin will be starting to be slowed up by ATC, and so will start to deploy flaps and hence as the first stage goes out, hey presto, you get the noise.

[barit1]

25 yrs ago I was sitting in a parked, shutdown aircraft when I heard a fairly loud groaning or foghorn sound - I wondered what the techs were doing to the plane that would make that noise.

Finally I looked out the window - and a TriStar was firing up about 500 m away. Great clouds of unburned Jet A emanating from those RB211-22B's! It was hard to believe that was the dominant noise on the ramp that morning, but I could have sworn it was from inside MY a/c.

[Kak Klaxon]

Thinking more about the strange noise I think its probably a trick of sound called the doppler effect and not related to config changes.

Good luck at LPBS, over and out.

[McFunkletrumpet]

NO NO NO KK

You can't have Over AND Out. One or tother. Roger????

[Atlantic-44]

Ah, that would be caused by GMU's - Groaning Master Units. A mod designed by Boeing to irritate an ex-employee that moved to....... errrrm........ let me think........ ah yes......... thats it............ he moved to Beckenham in Kent.